I've had the same Dyndolod and grass cache setup for awhile now and this recently started happening:
https://mega.nz/file/M7gCVRRb#KNDU4sT23jWG096jue9Z4Kbx6IVU0Nz98FNxkC6gLjA
I haven't modified INI files or made any changes that I suspect could lead to the LOD and grass unloading and reloading this way. Tried LOD Unloading mod, no help unfortunately but my issue does not appear related to fast travel.
Any ideas regarding what could cause this?